1. Field of the Invention
The present invention generally relates to a polarizing screen, a picture projector using the polarizing screen and a polarizing screen material used for the polarizing screen. More particularly, the present invention relates to the polarizing screen for use in association with a projection-type television receiver set utilizing a liquid crystal display device for providing a high-contrast projected picture comfortable to view, a projector system including the polarizing screen and a polarizing member for polarizing rays of light emitted from a light source, and a polarizing fabric and a polarizing fiber utilizable as material for the polarizing screen or the polarizing member.
2. Description of the Prior Art
A projection-type television receiver set is well known which generally comprises a source of televised pictures, a projector optics and a screen. The demand for the projection-type television receiver set utilizing a liquid crystal display device is now increasing. However, the projection-type television receiver set has a problem in that, since a televised picture projected by a projector is enlarged, the resolution of the projected picture is low enough to make it difficult for a viewer to enjoy looking the projected picture. The resolution and/or contrast of the projected picture are further lowered when the projection-type television receiver set is operated in a fairly bright room since the screen reflects external rays of light towards the position of the viewer.
Various attempts have, therefore, been made to improve the viewability of the screen such as disclosed in, for example, the Japanese Laid-open Patent Publications No. 62-266980 (published in 1987) and No. 64-77085 (publi. in 1989) and Laid-open Utility Model Publication No. 3-5147 (publi. in January, 1991). According to these prior attempts, the use has been made of a first polarizing film having a first polarizing direction and a second polarizing film having a second polarizing direction lying perpendicular to the first polarizing direction of the first polarizing film. The first polarizing film is disposed on a front surface of the screen facing towards the position of a television viewer and the second polarizing film is disposed around an indoor illuminator such as an indoor illuminating lamp, so that rays of light emitted from the indoor illuminator and polarized by the second polarizing film are absorbed by the first polarizing film thereby to provide a projected picture that is comfortable to look.
While most of the color projection-type television receiver sets now in use utilize a color picture projector comprising a set of bulky and heavy cathode ray tubes, it is a recent trend to employ a liquid crystal display device in place of the cathode ray tube. So far as the screen size of 60 inches or more is concerned, the use of the liquid crystal display device for the picture projector is generally considered advantageous.
However, while external rays of light such as sunlight and those originating from indoor illuminating lamps are not generally polarized, rays of light originating from the liquid crystal display device are linearly polarized. In view of this, the Japanese Laid-open Patent Publication No. 2-267536, published in 1990, suggests the use on the screen of a polarizing film capable of passing therethrough only projected rays of light polarized in a particular direction so that the external rays of light having a direction of polarization different from the particular direction of polarization of the projected rays of light can be absorbed by the screen, thereby suppressing any possible reduction in contrast of the projected picture and also to provide the sharp projected picture even in a bright environment.
The polarizing film according to any one of the above discussed prior art techniques is made of a stretched film of polymer such as, for example, poly(vinyl alcohol), absorbed with iodine or organic dichroic dyes of, for example, benzidine, dianisidine, tolidine or stilbene. Therefore, when it comes to the polarizing film having a relatively large surface area for use in the screen of a large screen size, it is not easy to stretch the film in required directions so as to have a required surface area. Where a plurality of small polarizing films are joined together so as to have the required surface area, the presence of joints of the small polarizing films may cause a reduction in image quality of the picture that is eventually projected. In addition, the prior art polarizing film makes it difficult to form thereon fine indentations that are generally required for adjustment of the viewing angle.
A polarizing member made up with fibers, not film, is disclosed in, for example, the Japanese Laid-open Patent Publications No. 51-149919, published in 1976, and No. 63-275787 published in 1988. The polarizing member disclosed therein is exclusively for use in clothing and any one of these publications has failed to suggest the use thereof in association with the projector screen.